I’ll be honest, I don’t use many. I was using a bootleg music ripping program that comes in an appimage, and I suspected the error was specific to appimages. I tried the example one from appimage.org, and it failed to open with a similar error, although less verbose:

Just now, I tried using an etcher AppImage and it works. So now I’m thinking it may just be coincidence. But I must have something wrong with my setup if the appimage used as a demo on the official site isn’t working, so it would be nice to get that resolved.

Edit: I installed zenity, which got rid of that error message. For my music program, all I’m getting now is a core dump, and with subsurface, I’m still getting

This application failed to start because it could not find or load the Qt platform plugin "xcb"
in "".

and then a core dump. So I have no idea if it’s the same issue causing both, but I am mainly just looking for help with getting subsurface to work, and I’ll see if it fixes the other thing.